It has previously been proposed--see U.S. Pat. No. 3,900,013, Vignozzie et al corresponds to German Disclosure Document DE-OS 23 14 447--to provide pulses representative of speed of an internal combustion engine, and then to integrate these pulses to obtain an integrated value which will be representative of engine speed. When the integrated value reaches a predetermined threshold level, control systems which limit the speed of the engine can be triggered or commanded to become effective. Such arrangements as proposed have the disadvantage that reliable operation of the limiting system requires an integrator with a relatively long time constant. Thus, the system cannot respond to rapid changes in speed tending to increase the speed of the engine to an undesired, or even unsafe level.